Resin for high-refractivity lenses and lenses made of same resin

ABSTRACT

Disclosed herein are a resin for high-refractivity lenses, formed by copolymerizing at least one nucleus-halogenated benzene dicarboxylate represented by the following general formula (I): ##STR1## wherein X means a chlorine or bromine atom, n is 2 or 4, m stands for 0 or 1 and R denotes a hydrogen atom or a methyl group with at least one unifunctional monomer having a refractive index of at least 1.55 as a homopolymer, capable of undergoing a radical polymerization and containing an aromatic ring as well as high-refractivity lenses made of such a resin. The lens-making resin according to this invention features a high refractive index, excellent processability such as superb grinding processability and high impact resistance, outstanding miscibility between the unifunctional monomer and bifunctional monomer upon copolymerization thereof, and minimized polymerization strain.

DESCRIPTION

1. Technical Field

This invention relates to a lens-making resin having a high refractiveindex and a lens made of the above resin.

2. Background Art

Plastic lenses have found increasing commercial utility as eyeglasslenses, camera lenses and other optical lenses in recent years, sincethey are lighter in weight, less fragile and more readily colored incomparison with inorganic glass lenses. As a resin which is currentlyused in a large volume for the above application, there is a resinobtained by the casting-polymerization of diethylene glycolbisallylcarbonate (hereinafter called "CR-39"). However, the refractiveindex (n_(d)) of the above resin is 1.50, which is smaller compared withthose of inorganic glass lenses (n_(d) =about 1.52). In order to achievethe same optical characteristics as glass lenses, it is necessary toincrease the central thickness, peripheral thickness and curvature ofeach plastic lens, thereby unavoidably making the plastic lens thickeras a whole. For this reason, there is an outstanding desire for thedevelopment of a lens-making resin having a still higher refractiveindex. As resins having high refractive indexes, there have already beenknown polycarbonate (n_(d) =1.58-1.59), polystyrene (n_(d) =1.58-1.60),etc. These resins are each a two-dimensional polymer structurally andthermoplastic. They are thus unsuitable for casting-polymerizationmethod which is suitable for production of articles in various modelssuch as fabrication of eyeglass lenses, and their post-moldingprocessings, especially, their rough-grinding and smoothing (hereinaftermerely referred to as "grinding") work is difficult. Therefore, use ofthese resins are presently limited to some sort of safety eyeglasses andthe like.

Accordingly, there is a strong desire for the development of alens-making resin which has a refractive index higher than that of thelens-making resin prepared by polymerizing CR-39, can becast-polymerized similar to CR-39 and does not make diamond-madegrindstones loaded owing to its three-dimensional crosslinking structurewhen grinding molded lens blanks. A variety of researches has alreadybeen carried out with a view toward developing a resin which would meetthe above-mentioned desire, resulting in proposals of resins obtained bycopolymerizing CR-39 and second monomers having refractive indexeshigher than that of CR-39 when measured as their respective homopolymers(see, Japanese Patent Laid-open Nos. 79353/1976, 7787/1978, 77686/1979,15118/1980 and 36601/1981). The refractive indexes of thethus-copolymerized resins are however inherently limited because theyemploy CR-39 as their principal components. It was thus difficult toobtain a resin having a high refractive index, for example, a refractiveindex of 1.55 or higher.

In order to obtain a resin having a still higher refractive index, it isurged to use a bifunctional monomer which can afford a homopolymerhaving a refractive index higher than that of CR-39. However, each ofbifunctional monomers which have been proposed to date resulted in apolymer having impact resistance much poorer compared with thehomopolymer of CR-39 when polymerized singly. Thus, some attempts havebeen made to improve the impact resistance of these bifunctionalmonomers by copolymerizing them with a unifunctional monomer. Here, eachmatching unifunctional monomer is required to have a high refractiveindex when measured as its homopolymer if one wants to obtain acopolymer having a high refractive index. For this reason, styrene or ahalogen-substituted styrene is presently used as such a unifunctionalmonomer. However, use of bifunctional monomers different from CR-39,which have heretofore been proposed, in combination with theabove-mentioned unifunctional monomers is accompanied by such drawbacksthat it tends to result in development of polymerization strain and isdifficult to obtain polymers having uniform refractivity distributionbecause there are considerable differences in polymerization reactivitybetween such bifunctional monomers and unifunctional monomers and theproportions of the bifunctional monomers and unifunctional monomerscannot be varied freely due to poor miscibility therebetween.

With the foregoing in view, the present inventors carried out anextensive research with a view toward making improvements to theabove-described drawbacks. As a result, it has been found that a resin,which has a high refractive index and excellent processability such asgrinding processability and superb impact resistance, exhibits excellentmiscibility between its starting unifunctional monomer and bifunctionalmonomer upon copolymerization thereof, is less susceptible of developingpolymerization strain and is thus suitable for use in the production ofhigh-refractivity lenses, can be obtained by copolymerizing a specificbifunctional monomer and a unifunctional monomer having a refractiveindex of at least 1.55 as a homopolymer, capable of undergoing a radicalpolymerization and containing an aromatic ring, leading to completion ofthis invention.

DISCLOSURE OF THE INVENTION

This invention therefore provides a resin for high-refractivity lenses,formed by copolymerizing at least one nucleus-halogenated benzenedicarboxylate represented by the following general formula (I): ##STR2##wherein X means a chlorine or bromine atom, n is 2 or 4, m stands for 0or 1 and R denotes a hydrogen atom or a methyl group with at least oneunifunctional monomer having a refractive index of at least 1.55 as ahomopolymer, capable of undergoing a radical polymerization andcontaining an aromatic ring. This invention also provides lenses made ofsuch a resin.

BEST MODE FOR CARRYING OUT THE INVENTION

The first monomer of this invention, namely, the nucleus-halogenatedbenzene dicarboxylate represented by the general formula (I) may beprepared by the esterification reaction between the acid chloride of itscorresponding nucleus-halogenated benzenedicarboxylic acid and allylalcohol or β-methylallyl alcohol or by the esterification reactionbetween the corresponding nucleus-halogenated benzenedicarboxylic acidand allyl chloroacetate or β-methylallyl chloroacetate in the presenceof triethylamine or the like. As specific examples of thenucleus-halogenated benzene dicarboxylate represented by the generalformula (I), may be mentioned:

Bisallyl 2,4-dichloroterephthalate;

Bis(β-methylallyl) 2,4-dichloroterephthalate;

Bis(allyloxycarbonylmethyl) 2,4-dichloroterephthalate;

Bis(β-methylallyloxycarbonylmethyl) 2,4-dichloroterephthalate;

Bisallyl 2,4-dibromoterephthalate;

Bis(β-methylallyl) 2,4-dibromoterephthalate;

Bis(allyloxycarbonylmethyl) 2,4-dibromoterephthalate;

Bis(β-methylallyloxycarbonylmethyl) 2,4-dibromoterephthalate;

Bisallyl tetrachloroterephthalate;

Bis(β-methylallyl) tetrachloroterephthalate;

Bis(allyloxycarbonylmethyl) tetrachloroterephthalate;

Bis(β-methylallyloxycarbonylmethyl) tetrachloroterephthalate;

Bisallyl tetrabromoterephthalate;

Bis(β-methylallyl) tetrabromoterephthalate;

Bis(allyloxycarbonylmethyl) tetrabromoterephthalate;

Bis(β-methylallyloxycarbonylmethyl) tetrabromoterephthalate;

Bisallyl tetrachlorophthalate;

Bis(β-methylallyl) tetrachlorophthalate;

Bis(allyloxycarbonylmethyl)tetrachlorophthalate;

Bis(β-methylallyloxycarbonylmethyl) tetrachlorophthalate;

Bisallyl tetrabromophthalate;

Bis(β-methylallyl) tetrabromophthalate;

Bis(allyloxycarbonylmethyl) tetrabromophthalate; and

Bis(β-methylallyloxycarbonylmethyl) tetrabromophthalate.

The ester represented by the general formula (I) is subjected tocopolymerization in the present invention, using as a second monomer aunifunctional monomer having a refractive index of at least 1.55 as ahomopolymer, capable of undergoing a radical polymerization andcontaining an aromatic ring because the impact resistance of a polymerobtained by polymerizing the ester alone is too small. Any monomer maybe used as the above-mentioned second monomer so long as it satisfiesthe above-described requirements. However, when it was subjected tocopolymerization with the ester represented by the general formula (I)to obtain a resin, it is not preferable the resin exhibits poor lightresistance, that is, it takes a color extremely when it was exposed toultraviolet rays. As representative specific examples such monomers thatit is generally preferred to use may be mentioned:

Acrylates or Methacrylates Containing Aromatic Rings

For example, phenyl acrylate, phenyl methacrylate, nucleus-chlorinatedphenyl acrylates, nucleus-chlorinated phenyl methacrylates,nucleus-brominated phenyl acrylates, nucleus-brominated phenylmethacrylates, benzyl acrylate, benzyl methacrylate, nucleus-chlorinatedbenzyl acrylates, nucleus-chlorinated benzyl methacrylates,nucleus-brominated benzyl acrylates, nucleus-brominated benzylmethacrylates, α-naphthyl acrylates, α-naphthyl methacrylates,β-naphthyl acrylates and β-naphthyl methacrylates.

Styrenes

For example, styrene, nucleus-chlorinated styrenes andnucleus-brominated styrenes.

Vinyl Naphthalenes

For example, 1-vinyl naphthalene and 2-vinyl naphthalene.

Among these, in order to obtain a resin which has superb impactresistance, it is preferred to use phenyl methacrylate,nucleus-halogenated methacrylates, benzyl methacrylate ornucleus-halogenated benzyl methacrylates.

In the present invention, the proportion of each ester represented bythe general formula (I) cannot be limited to any specific value or rangebecause its preferred proportion may vary depending on the type of theester. However, the ester of the general formula (I) may be used at aproportion of 10-80 wt. % or, preferably 10-70 wt. %. If the ester isincorporated at any proportion lower than 10 wt. %, the resultant,copolymerized resin will have an extremely low surface hardness. Anyproportions in excess of 80 wt. % are not preferred because the impactresistance will be lowered. Accordingly, it is preferred to use one ormore of the above-described second monomers, which are copolymerizedwith the ester represented by the general formula (I), at a totalproportion of 20-90 wt. %.

Furthermore, no particular limitation is vested on the type of a radicalpolymerization initiator which is to be used upon conducting acopolymerization so as to obtain a lens-making resin according to thisinvention. It is thus preferable to use, at a proportion of 0.01-5 wt.%, a conventional peroxide such as benzoyl peroxide, p-chlorobenzoylperoxide, diisopropyl peroxycarbonate, di-2-ethylhexyl peroxycarbonateor tertiary butyl peroxypivalate or a known azo compound such asazobisisobutyronitrile.

The lens-making resin according to this invention can be prepared bysubjecting a mixture of at least one ester represented by the generalformula (I), at least one of the above-described second monomer and aradical polymerization initiator to the known casting-polymerizationmethod, in other words, pouring the mixture into a mold formed of agasket or spacer and a glass-made or metallic mold and polymerizing andhardening the mixture by heating it at temperatures in the range of50°-120° C. or irradiating ultraviolet rays to the mixture. Here, it maybe possible to incorporate one or more appropriate additives such asultraviolet stabilizer, antioxidant, coloring inhibitor, fluorescent dyeand/or the like to the mixture prior to its polymerization as needed.

The thus-obtained lens-making resin according to this invention has ahigh refractive index, excellent processability such as superb grindingprocessability and outstanding impact resistance and can thus be usedfor eyeglass lenses, camera lenses and other optical lenses.

Some examples of this invention will hereinafter be described, in whichall designations of "part" or "parts" mean part or parts by weight andall designations of "%" mean wt. %. Incidentally, the following testingmethods were employed to determine the refractive indexes, grindingprocessability, impact resistance and extents of yellowing upon exposureto ultraviolet rays of the lens-making resins obtained in the examples.

Refractive Indexes:

Measured at 20° C. by an Abbe refractometer.

Processability:

Each molded lens blank was ground by a grinding machine designed toprocess eyeglass lenses. Samples bearing smooth ground surfaces werejudged acceptable and marked by circles ( ).

Impact Resistance:

A falling ball impact test was carried out in accordance with the FDAstandards on planar plates having the thickness of 2 mm at theircenters. Unbroken samples were judged as acceptable and marked bycircles ( ).

Ultraviolet Resistance Test:

Lens samples were placed in a Weather-O-Meter equipped with a Sunshinecarbon arc-lamp. After an elapsed time of 200 hours, the lens sampleswere taken out of the Weather-O-Meter and their hues were compared withtheir hues prior to the testing in the Weather-O-Meter. Results wereevaluated and marked as follows:

. . . Unchanged.

Δ . . . Slightly yellowed.

× . . . Yellowed.

SYNTHESIS EXAMPLE 1

To a liquid mixture consisting of 34 parts of tetrachloroterephthalicacid dichloride, 34 parts of carbon tetrachloride and 3.4 parts oftriethylamine, were added dropwise 15 parts of allyl alcohol. Theresultant mixture was heated until carbon tetrachloride started toreflux. The mixture was maintained at the temperature for 5 hours. Afterallowing the reaction mixture to cool, the liquid reaction mixture waspoured in a separation funnel and washed with dilute hydrochloric acidand water. The organic layer was then dried with calcium chloride andthen filtered. Activated carbon was added to the filtrate and mixedtherewith. The resultant mixture was filtered and the resulting filtratewas concentrated to give 28 parts of diallyl tetrachloroterephthalate asa colorless, clear, semi-solid matter (hereinafter called "Compound A").It was recrystallized from ligroin, thereby obtaining 23 parts ofacicular crystals (m.p. 71°-73° C.).

Elementary analysis: Calculated for C₁₄ H₁₀ Cl₄ O₄ : C, 43.79; H, 2.62;Cl, 36.93. Found: C, 43.69; H, 2.53; Cl, 36.99.

NMR: δCDCl₃ =4.90 (4H, d), 5.35 (4H, t), 5.80˜6.20 (2H, m).

SYNTHESIS EXAMPLE 2

To a liquid mixture consisting of 19.3 parts of tetrabromoterephthalicacid and 40 parts of isopropyl alcohol, were added with stirring 13parts of a 50% aqueous solution of caustic potash. After continuouslymixing the thus-obtained mixture for 30 minutes, 12.6 parts of allylbromide and 1.0 part of triethylamine were added. The resulting mixturewas heated until isopropanol started to reflux. The mixture wasmaintained at the temperature for 8 hours. After allowing the resultingreaction mixture to cool, the liquid reaction mixture was concentratedunder reduced pressures, followed by an addition of 50 parts ofchloroform to dissolve the residue. The resultant solution was poured ina separation funnel and then washed with an aqueous solution of sodiumbicarbonate and thereafter with water. The organic layer wasconcentrated and the resultant white solid was recrystallized from ethylacetate, thereby obtaining 12 parts of diallyl tetrabromoterephthalate(hereinafter called "Compound B") as white irregular crystals (m.p.125°-127° C.).

Elementary analysis: Calculated for C₁₄ H₁₀ Br₄ O₄ : C, 29.90; H, 1.79;Br, 56.90. Found: C, 29.89; H, 1.61; Br, 56.90.

NMR: δCDCl₃ =4.90 (4H, d), 5.40 (4H, t), 5.80˜6.25 (2H, m).

SYNTHESIS EXAMPLE 3

The procedures of Synthesis Example 1 were followed except that 34 partsof tetrachlorophthalic acid dichloride were used in lieu of 34 parts oftetrachloroterephthalic acid dichloride, thereby obtaining 26 parts ofdiallyl tetrachlorophthalate (hereinafter called "Compound C") as acolorless, clear and viscous liquid. A portion of the liquid wasrecrystallized from ligroin to give columnar crystals (m.p. 71°-72° C.).

Elementary analysis: Calculated for C₁₄ H₁₀ Cl₄ O₄ : C, 43.79; H, 2.62;Cl, 36.93. Found: C, 43.66; H, 2.58; Cl, 36.87.

NMR: δCDCl₃ =4.85 (4H, d), 5.40 (4H, t), 5.80˜6.25 (2H, m).

SYNTHESIS EXAMPLE 4

The procedures of Synthesis Example 2 were repeated except that 13.0parts of 2,4-dibromoterephthalic acid and 14.1 parts of β-methylallylbromide were respectively used instead of 19.3 parts oftetrabromoterephthalic acid and 12.6 parts of allyl bromide. Theresulting organic layer was treated with activated carbon and thenconcentrated, thereby obtaining 13 parts of bis(β-methylallyl)2,4-dibromoterephthalate (hereinafter called "Compound D") as a glassysolid.

Elementary analysis: Calculated for C₁₆ H₁₆ Br₂ O₄ : C, 44.47; H, 3.73;Br, 36.99. Found: C, 43.95; H, 3.92; Br, 37.05.

NMR: δCDCl₃ =7.30 (2H, s), 5.00 (4H, d), 1.75 (6H, s).

SYNTHESIS EXAMPLE 5

To a liquid mixture consisting of 24 parts of tetrabromoterephthalicacid and 60 parts of chloroform, were dropped with stirring 20 parts ofallyl chloroacetate. Thereafter, 13 parts of triethylamine were addeddropwise while cooling the resulting mixture at 15°-20° C. The mixturewas heated until chloroform started to reflux. At the same temperature,the mixture was maintained for 8 hours. After allowing the liquidreaction mixture to cool, it was poured in a separation funnel andwashed first with dilute hydrochloric acid and then with water. Theorganic layer was concentrated under reduced pressures and the resultingwhite solid was recrystallized from ethyl acetate, thereby obtaining 25parts of bis(allyloxycarbonylmethyl) tetrabromoterephthalate(hereinafter called "Compound E") as white irregular crystals. (m.p.146°-148° C.).

Elementary analysis: Calculated for C₁₈ H₁₄ Br₄ O₈ : C, 31.89; H, 2.08;Br, 47.15. Found: C, 31.83; H, 2.12; Br, 47.08.

NMR: δCDCl₃ =4.70 (4H, d), 4.88 (4H, s), 5.33 (4H, t), 5.75˜5.18 (2H,m).

SYNTHESIS EXAMPLE 6

The procedures of Synthesis Example 2 were repeated except that 19.3parts of tetrabromophthalic acid and 9.2 parts of β-methyl-allylchloride were employed instead of 19.3 parts of tetrabromoterephthalicacid and 12.6 parts of allyl bromide respectively. The thus-obtainedwhite solid was recrystallized from ligroin to obtain 10 parts ofbis(β-methyl-allyl) tetrabromophthalate (hereinafter called "CompoundF") as colorless columnar crystals (m.p. 80°-82° C.).

Elementary analysis: Calculated for C₁₆ H₁₄ Br₄ O₄ : C, 32.58; H, 2.39;Br, 54.18. Found: C, 32.55; H, 2.43; Br, 53.98.

NMR: δCDCl₃ =1.83 (6H, s), 4.72 (4H, s), 5.06 (4H, d).

EXAMPLE 1

A liquid mixture, which had been obtained by mixing 50 parts of diallyltetrachlorophthalate, 50 parts of phenyl methacrylate and 0.2 part ofbenzoyl peroxide was poured into a mold which was formed of a glass moldand a polyethylene gasket. It was held at 60° C. for 24 hours, at 80° C.for 2 hours and at 100° C. for 2 hours to carry out the copolymerizationof the contents. The thus-formed resin was next taken out of the mold,on which a refractivity measurement, processability test, impactresistance test and ultraviolet resistance test were conducted. Asresults of such a measurement and tests, it was found that thethus-obtained colorless transparent lens had the refractive index of1.585 and good ultraviolet ray resistance.

EXAMPLES 2-14

In the same manner as in Example 1, monomers were copolymerized atdifferent proportions to prepare lenses. Results are shown in Table 1,together with results of Comparative Examples 1-5.

                                      TABLE 1                                     __________________________________________________________________________                                        Ultraviolet                               Composition      Refractive                                                                          Grinding                                                                             Impact                                                                              Resistance                                of Polymers  (parts)                                                                           Index n.sub.d.sup.20                                                                Processability                                                                       Resistance                                                                          Test                                      __________________________________________________________________________    Example                                                                       1    A/PhMA  (50/50)                                                                           1.583 O      O     O                                         2    A/p-BrPhMA                                                                            (40/60)                                                                           1.604 O      O     O                                         3    A/o-ClSt                                                                              (70/30)                                                                           1.600 O      O     O                                         4    B/PhMA  (50/50)                                                                           1.591 O      O     O                                         5    B/o-ClBMA                                                                             (40/60)                                                                           1.594 O      O     O                                         6    B/o-ClSt                                                                              (70/30)                                                                           1.606 O      O     O                                         7    C/PhMA  (50/50)                                                                           1.585 O      O     O                                         8    C/o-ClBMA                                                                             (40/60)                                                                           1.590 O      O     O                                         9    D/PhMA  (50/50)                                                                           1.584 O      O     O                                         10   D/p-BrPhMA                                                                            (40/60)                                                                           1.598 O      O     O                                         11   E/PhMA  (50/50)                                                                           1.573 O      O     O                                         12   E/BrSt  (70/30)                                                                           1.602 O      O     O                                         13   F/PhMA  (50/50)                                                                           1.600 O      O     O                                         14   F/St    (70/30)                                                                           1.617 O      O     O                                         Compar-                                                                       ative                                                                         Example                                                                       1    CR-39   (100)                                                                             1.498 O      O     O                                         2    CR-39/PhMA                                                                            (50/50)                                                                           1.532 O      O     O                                         3    DAP/PhMA                                                                              (50/50)                                                                           1.536 O      O     O                                         4    CR-39/o-ClSt                                                                          (70/30)                                                                           1.533 ×                                                                              O     Δ                                   5    DAP/BrSt                                                                              (70/30)                                                                           1.544 ×                                                                              ×                                                                             Δ                                   __________________________________________________________________________     Note:                                                                         PhMA --  Phenylmethacrylate.                                                  oClBMA --  oChlorobenzylmethacrylate.                                         pBrPhMA --  pBromophenylmethacrylate.                                         Br--St --  Bromostyrene (oisomer: 70 wt. %; pisomer: 30 wt. %).               oClSt --  oChlorostyrene.                                                     DAP --  Diallyl phthalate.                                                    St --  Styrene.                                                          

We claim:
 1. A resin for high-refractivity lenses, formed bycopolymerizing 10 to 70 weight percent of at least onenucleus-halogenated benzene dicarboxylate having the following formula(I): ##STR3## wherein X is a chlorine atom or a bromine atom, n is 2 or4, m is 0 or 1 and R is a hydrogen atom or a methyl group, with 30 to 90weight percent of at least one unifunctional monomer which has arefractive index of at least 1.55 as a homopolymer, is capable ofundergoing a radical polymerization and contains an aromatic ring. 2.Resin as claimed in claim 1 wherein, in formula (I), X is chlorine. 3.Resin as claimed in claim 1 wherein, in formula (I), X is bromine. 4.Resin as claimed in claim 1 wherein, in formula (I), R is hydrogen. 5.Resin as claimed in claim 1 wherein, in formula (I), R is methyl. 6.Resin as claimed in claim 1 wherein, in formula (I), m is
 0. 7. Resin asclaimed in claim 1 wherein, in formula (I), m is
 1. 8. Resin as claimedin claim 1 wherein the unifunctional monomer is an acrylate containingan aromatic ring, a methacrylate containing an aromatic ring, a styreneor a vinyl naphthalene.
 9. Resin as claimed in claim 1 wherein theunifunctional monomer is phenyl acrylate, phenyl methacrylate, anucleus-chlorinated phenyl acrylate, a nucleus-chlorinated phenylmethacrylate, a nucleus-brominated phenyl acrylate, a nucleus-brominatedphenyl methacrylate, benzyl acrylate, benzyl methacrylate, anucleus-chlorinated benzyl acrylate, a nucleus-chlorinated benzylmethacrylate, a nucleus-brominated benzyl acrylate, a nucleus-brominatedbenzyl methacrylate, an α-naphthyl acrylate, an α-naphthyl methacrylate,β-naphthyl acrylate, a β-naphthyl methacrylate, styrene, anucleus-chlorinated styrene, a nucleus-brominated styrene, 1-vinylnaphthalene or 2-vinyl naphthalene.
 10. A lens comprising a copolymer of10 to 70 weight percent of at least one nucleus-halogenated benzenedicarboxylate having the following formula (I): ##STR4## wherein X is achlorine atom or a bromine atom, n is 2 or 4, m is 0 or 1 and R is ahydrogen atom or a methyl group, and 30 to 90 weight percent of at leastone unifunctional monomer, which has a refractive index of at least 1.55as a homopolymer, is capable of undergoing a radical polymerization andcontains an aromatic ring.
 11. Lens as claimed in claim 10 wherein, informula (I), X is chlorine.
 12. Lens as claimed in claim 10 wherein, informula (I), X is bromine.
 13. Lens as claimed in claim 10 wherein, informula (I), R is hydrogen.
 14. Lens as claimed in claim 10 wherein, informula (I), R is methyl.
 15. Lens as claimed in claim 10 wherein, informula (I), m is
 0. 16. Lens as claimed in claim 10 wherein, in formula(I), m is
 1. 17. Lens as claimed in claim 10 wherein the unifunctionalmonomer is an acrylate containing an aromatic ring, a methacrylatecontaining an aromatic ring, a styrene or a vinyl naphthalene.
 18. Lensas claimed in claim 10 wherein the unifunctional monomer is phenylacrylate, phenyl methacrylate, a nucleus-chlorinated phenyl acrylate, anucleus-chlorinated phenyl methacrylate, a nucleus-brominated phenylacrylate, a nucleus-brominated phenyl methacrylate, benzyl acrylate,benzyl methacrylate, a nucleus-chlorinated benzyl acrylate, anucleus-chlorinated benzyl methacrylate, a nucleus-brominated benzylacrylate, a nucleus-brominated benzyl methacrylate, an α-naphthylacrylate, an α-naphthyl methacrylate, a β-naphthyl acrylate, aβ-naphthyl methacrylate, styrene, a nucleus-chlorinated styrene, anucleus-brominated styrene, 1-vinyl naphthalene or 2-vinyl naphthalene.